The good news: There are more than 3 trillion trees on Earth. The bad news: There has been a 46 percent drop in the number of trees since the dawn of human civilization.

The tree census was done by a team of researchers, using satellite imagery, forest inventories and technology to map the number of trees on a square kilometer level.

“Trees are among the most prominent and critical organisms on Earth, yet we are only recently beginning to comprehend their global extent and distribution,” said the study's lead author, Thomas Crowther, with the Yale School of Forestry & Environmental Studies (F&ES).

Crowther said he was surprised that the census found so many trees.

Previous estimates had put the number of trees at 400 billion, while Crowther’s study came up with 3.04 trillion, or 422 trees per person.

Trees are important for storing carbon, improving air and water quality, and many other things humans depend on.

Where the Trees Are

The sub-Arctic regions of Russia, Scandinavia and North America have the highest density of trees, while the tropics account for the largest number, about 43 percent of the world’s trees.

Humans are the biggest influence of tree numbers worldwide, according to Crowther, saying that tree density falls precipitously as the human population grows and that deforestation and other human activities account for a loss of 15 billion trees annually.

“We’ve nearly halved the number of trees on the planet, and we’ve seen the impacts on climate and human health as a result,” Crowther said. “This study highlights how much more effort is needed if we are to restore healthy forests worldwide.”